We present a full sky 100 micron map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 micron and 240 micron data, we have constructed a map of the dust temperature, so that the 100 micron map can be converted to a map proportional to dust column density. The dust temperature varies from 17 K to 21 K, which is modest but does modify the estimate of the dust column by a factor of 5. The result of these manipulations is a map with DIRBE-quality calibration and IRAS resolution. A wealth of filamentary detail is apparent on many different scales at all Galactic latitudes. In high latitude regions, the dust map correlates well with maps of HI emission, but deviations are coherent in the sky and are especially conspicuous in regions of saturation of HI emission toward denser clouds or the formation of H2 in molecular clouds. In contrast, high-velocity HI clouds are deficient in dust emission, also as expected.
To generate the full sky dust maps, we must first remove zodiacal light contamination as well as a possible cosmic infrared background (CIB). This is done via a regression analysis of the 100 micron DIRBE map against the Leiden-Dwingeloo map of HI emission, with corrections for the zodiacal light via a suitable expansion of the DIRBE 25 micron flux. This procedure removes virtually all traces of the zodiacal foreground. For the 100 micron map no signficant CIB is detected, but in the 140 micron and 240 micron maps, where the zodiacal contamination is weaker, we detect the CIB at surprisingly high flux levels of 30 +/- 8 nW/m2/sr at 140\micron, and 16 +/- 3.4 nW/m2/sr at 240 micron (95% confidence), which is an integrated flux approximately twice as large as measured for the Hubble Deep Field.
The primary use of these maps is likely to be as a new estimator of Galactic extinction. To calibrate our maps, we assume a standard reddening law, and use the colors of elliptical galaxies to measure the reddening per flux density of 100 micron emission. We find consistent calibration using the (B-R) color distribution of a sample of 106 brightest cluster ellipticals, as well as a sample of 389 ellipticals with (B-V) and Mg2 index measurements. For the latter sample, we use the correlation of intrinsic B-V versus Mg linestrength to greatly tighten the power of the test. We demonstrate that the new maps are twice as accurate as the older Burstein-Heiles reddening estimates in regions of low and moderate reddening. The maps are expected to be significantly more accurate in regions of high reddening. These dust maps will also be useful for estimating millimeter emission that contaminates CMBR experiments and for estimating soft X-ray absorption.
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